Modern mobile telecommunications standards continue to demand increasingly greater rates of data exchange (data rates). One way to achieve a high data rate in a mobile device is through the use of carrier aggregation. Carrier aggregation allows a single mobile device to aggregate bandwidth across one or more operating bands in the wireless spectrum. The increased bandwidth achieved as a result of carrier aggregation allows a mobile device to obtain higher data rates than have previously been available.
FIG. 1 shows a table describing a number of wireless communications bands in the wireless spectrum. One or more of the wireless communications bands may be used, for example, in a CDMA, GSM, LTE, or LTE-advanced equipped mobile device. The first column indicates the operating band number for each one of the operating bands. The second and third columns indicate the uplink and downlink frequency bands for each one of the operating bands, respectively. Finally, the fourth column indicates the duplex mode for each one of the operating bands. In non-carrier aggregation configurations, a mobile device will generally communicate using a single portion of the uplink or downlink frequency bands within a single operating band. In carrier aggregation applications, however, a mobile device may aggregate bandwidth across a single operating band or multiple operating bands in order to increase the data rate of the device.
FIG. 2A shows a diagram representing a conventional, non-carrier aggregation configuration for a mobile device. In the conventional configuration, a mobile device communicates using a single portion of the wireless spectrum 10 within a single operating band 12. Under the conventional approach, the data rate of the mobile device is constrained by the limited available bandwidth.
FIGS. 2B-2D show diagrams representing a variety of carrier aggregation configurations for a mobile device. FIG. 2B shows an example of contiguous, intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 14A and 14B are located directly adjacent to one another and are in the same operating band 16. FIG. 2C shows an example of non-contiguous intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 18A and 18B are located within the same operating band 20, but are not directly adjacent to one another. Finally, FIG. 2D shows an example of inter-band carrier aggregation, in which the aggregated portions of the wireless spectrum 22A and 22B are located in different operating bands 24, 26. A modern mobile device should be capable of supporting each one of the previously described carrier aggregation configurations.
The use of carrier aggregation may pose unique problems for the front end circuitry in a mobile device. For instance, a mobile device using carrier aggregation may require two or more antennas. The use of more than one antenna may complicate the design of the front-end switching circuitry within the mobile device. Additionally, the use of carrier aggregation across certain operating bands may cause undesirable interference between transmit and receive circuitry in a mobile device front end that renders the mobile device unusable in these operating bands.
FIG. 3 shows conventional front end circuitry 28 for use in a mobile terminal. The front end circuitry 28 includes antenna switching circuitry 30, a diplexer 32, and an antenna 34. The antenna switching circuitry 30 includes low band switching circuitry 36 and high band switching circuitry 38. The low band switching circuitry 36 is adapted to couple one of a first plurality of RF front end ports 40 to the antenna 34 through the diplexer 32. The high band switching circuitry 38 is adapted to couple one of a second plurality of RF front end ports 42 to the antenna 34 through the diplexer 32. The diplexer 32 includes a low band port 44 coupled to the low band switching circuitry 36, a high band port 46 coupled to the high band switching circuitry 38, and an antenna port 48 coupled to the antenna 34. The diplexer 32 is adapted to pass high band signals falling within a high pass band between the high band port 46 and the antenna port 48, pass low band signals falling within a low pass band between the low band port 44 and the antenna port 48, and attenuate signals outside of the high and low pass bands. Although effective at selectively placing the antenna 34 in communication with the appropriate RF front end port, the conventional front end circuitry 28 shown in FIG. 3 is not suitable for carrier aggregation applications that require multiple antennas.
FIG. 4 shows conventional front end circuitry 50 for use in a mobile terminal with two antennas. The front end circuitry 50 includes antenna switching circuitry 52, a first diplexer 54A, a second diplexer 54B, a first antenna 56A, and a second antenna 56B. The antenna switching circuitry 52 includes first antenna switching circuitry 52A and second antenna switching circuitry 52B. The first antenna switching circuitry 52A includes first low band switching circuitry 58, first high band switching circuitry 60, second low band switching circuitry 62, and second high band switching circuitry 64. The first low band switching circuitry 58 and the first high band switching circuitry 60 are adapted to selectively couple one of a first plurality of RF front end ports 66 to the second antenna switching circuitry 52B through the first diplexer 54A. The second low band switching circuitry 62 and the second high band switching circuitry 64 are adapted to selectively couple one of a second plurality of RF front end ports 68 to the second antenna switching circuitry 52B through the second diplexer 54B. The second antenna switching circuitry 52B includes antenna selection circuitry 70, which is adapted to selectively place the first antenna 56A and the second antenna 56B in communication with either the first diplexer 54A or the second diplexer 54B.
The antenna switching circuitry 52 may comprise a plurality of transistors and other assorted passive components. As is well known in the art, non-linearity of the transistors and other passive components within the antenna switching circuitry 52 may generate harmonic distortion about a passing signal. In certain carrier aggregation configurations, the generated harmonic distortion can cause desensitization of receive circuitry in the conventional front end circuitry 50 illustrated in FIG. 4. For example, the conventional front end circuitry 50 may be unusable in a carrier aggregation configuration using bands 3 and 8 (CA 3-8). In a CA 3-8 configuration, the conventional front end circuitry 50 will couple one of the second plurality of RF front end ports 68 corresponding with the band 8 transmit port to the antenna selection circuitry 70 in order to transmit a carrier signal between 880-915 MHz. As the carrier signal passes through the first low band switching circuitry 58, harmonic distortion is generated. The carrier signal and harmonic distortion travel through the first diplexer 54A, where the harmonic distortion is effectively filtered. However, as the carrier signal travels through the antenna selection circuitry 70, additional harmonic distortion is generated.
Because at least a portion of the second harmonic of the band 8 uplink band (1760-1830 MHz) falls within the band 3 downlink band (1805-1880 MHz), components of the harmonic distortion about the second harmonic are within the high pass band of the first diplexer 54A, and a portion of the harmonic distortion will be delivered to the first high band switching circuitry 60. Further, because the front end circuitry 50 is configured to simultaneously transmit on band 8 and receive on band 3, one of the first plurality of RF front end ports 66 corresponding with the band 3 receive port will be coupled to the first diplexer 54A through the first high band switching circuitry 60. Accordingly, a portion of the distorted band 8 transmit signal about the second harmonic will be delivered to the band 3 receive circuitry, where it will cause desensitization. Additionally, the harmonic distortion in the carrier signal will be presented to the antennas 56A and 56B, thereby degrading the quality of the wireless signal. As a result of the desensitization of the receiver circuitry, the performance of the front end circuitry 50 illustrated in FIG. 4 may suffer in a CA 3-8 configuration.
As an additional example, the conventional front end circuitry 50 will also experience problems in carrier-aggregation applications using bands 4 and 17 (CA 4-17), because the third harmonic of a band 17 transmit signal (2112-2148 MHz) falls within a band 4 receive signal (2110-2155 MHz). The problem with the conventional front end circuitry 50 may occur in any carrier aggregation configuration using operating bands in which the harmonic components of the carrier signal fall within the frequency band of the receive signal. The limited combination of operating bands usable in a carrier aggregation configuration by the conventional front end circuitry 50 illustrated in FIG. 4 may impede the performance and versatility of a mobile device. Accordingly, front end switching circuitry for a mobile device with two or more antennas is needed that is suitable for carrier aggregation applications across all bands.
FIG. 5 shows a conventional diplexer 72 for use in the front end circuitry 28 and 50 shown in FIGS. 3 and 4. The conventional diplexer 72 is based on a fourth order Butterworth response, and includes an antenna port 74, a low band port 76, a high band port 78, a high pass filter 80, and a low pass filter 82. The high pass filter 80 includes a first high band inductor L1_HB coupled between the high band port 78 and ground, a first high band capacitor C1_HB coupled between the high band port 78 and a first high band node 81, a second high band inductor L2_HB coupled between the first high band node 81 and ground, and a second high band capacitor C2_HB coupled between the first high band node 81 and the antenna port 74. The low pass filter 82 includes a first low band capacitor C1_LB coupled between the low band port 76 and ground, a first low band inductor L1_LB coupled between the low band port 76 and a first low band node 83, a second low band capacitor C2_LB coupled between the first low band node 83 and ground, and a second low band inductor L2_LB coupled between the first low band node 83 and the antenna port 74. The conventional diplexer 72 is designed to pass high band signals falling within a high pass band between the antenna port 74 and the high band port 78, pass low band signals falling within a low pass band between the antenna port 74 and the low band port 76, and attenuate signals outside of the high and low pass bands. The conventional diplexer 72 allows a mobile terminal to transmit and receive a high band signal and a low band signal simultaneously, thereby increasing the data rate of the mobile device. Although effective at separating low and high band signals, the conventional diplexer 72 is limited to fixed pass bands for the low and high band signals. In certain carrier aggregation applications, the rigidity of the conventional diplexer 72 may degrade the performance of a mobile device into which it is incorporated. Carrier aggregation applications may demand more precise control over the high and low pass bands, greater stop band attenuation, and lower insertion loss. To achieve the desired pass and stop bands, a seventh or eighth order Butterworth response may be required according to the conventional design. Such a high order filter would be complex to implement, and would further introduce a high amount of insertion loss into the signal path to the antenna. Accordingly, a diplexer is needed that is capable of providing the necessary pass bands for the high band and low band signals while maintaining a desirable stop band attenuation and insertion loss for carrier aggregation applications.